Thyroid hormone plasmatic levels in rats treated with serotonin in acute and chronic way.
Many experiments show that serotonin (5-HT) controls thyroidal function at hypothalamic level, inhibiting the TRH secretion. The majority of experiments are done in an acute way, consisting of a single serotonin dose injected intraperitoneally (i.p.) or intracerebroventricularly (ic) with the effect registered after a short time (usually 1 h) as in normal environmental conditions similar to the TSH stimulation test, that consists of transfer of the experimental animals from 30 degrees C to 4 degrees C for 30 min, thus inducing stimulation of the hypothalamus-hypophysis-thyroid axis. The aim of the present research was to study the correlation between 5-HT and the thyroidal function, measuring plasmatic thyroid hormone levels in rats i.p. treated in chronic (injected daily for 10 days with different doses of 5-HT), and in acute way (after 1 h from a single 2.0 mg/kg bw 5-HT dose) in normal environmental conditions to evidence the serotonin site action activity outside the blood-brain barrier. The results of the chronic experiment show an inhibitory effect of 5-HT, on T3 and T4 plasmatic level, only when it is injected at medium doses (0.2 and 0.4 mg/kg bw for T3, and 0.2 for T4), while the results of the acute experiment do not evidence any modification. These results show that in normal environmental conditions the outside 5-HT site action is active only when the 5-HT is injected chronically at defined doses, probably for a down-regulation phenomenon.
Brizzi
G
G
Department of Human Physiology and Integrated Biological Functions, Second University of Naples, Italy.
Carella
C
C
Foglia
M C
MC
Frigino
M
M
D000818:Animals; D004305:Dose-Response Relationship, Drug; D007274:Injections, Intraperitoneal; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D012701:Serotonin / Q000008:administration & dosage / Q000494:pharmacology* / Q000502:physiology; D013974:Thyroxine / Q000097:blood*; D013997:Time Factors; D014284:Triiodothyronine / Q000097:blood*
D014284:Triiodothyronine; D012701:Serotonin; D013974:Thyroxine